Author Topic: Solder mask oversizing for various components?  (Read 1163 times)

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Offline FaringdonTopic starter

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Solder mask oversizing for various components?
« on: June 26, 2021, 12:56:35 pm »
Hi,
The following Micro USB connector (below) has a pad to pad gap of 0.15mm in places.  Would you say it is possible to get  solder resist between such pads? (to stop shorting between pads at solder  bath  time).
If it is possible,(to get solder resist between the pads)  then the solder mask oversize would be very small round the pad. Such an oversize would generally not be applicable to other parts on the board (eg 1206 resistors). A 1206 resistor would generally have a 0.14mm solder mask oversize.
So that means you have different solder mask oversizing for different pads on the PCB…..the problem is that most PCB layout programs cannot handle such things (ie they can only give one solder mask oversize, and apply this to the entire board).
So how do you manage this situation?
Do you simply define your solder resist to be the same size as whichever pad, and then hope that the PCB manufacturer does a good (custom) solder mask oversize for every single pad?

How many people subscribe to the theory, that when a SMD part is below a certain size, then its simply a bad idea to use any solder resist, because the solder resist may hold the part up off the board and prevent it from “settling” onto the pads at solder bath time?
….if you subscribe to this, then how small does an smd part have to be before you say it should  not have any solder resist?

Micro USB connector (2173157-3 (TE))
https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Customer+Drawing%7F2173157%7FA1%7Fpdf%7FEnglish%7FENG_CD_2173157_A1_2173157-C_revA1.pdf%7F2173157-3
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Offline Skashkash

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Re: Solder mask oversizing for various components?
« Reply #1 on: June 26, 2021, 01:15:54 pm »
Jlcpcb (as an example) has a minimum solder mask sliver as .05mm (wrong)
I'm assuming that's for their standard service.

https://jlcpcb.com/capabilities/Capabilities

I do prefer to have solder mask between pins if I can get it. In my experience it does seem to help with avoiding shorts/bridging. For very fine pitch parts like some QFNs, it's less helpful.  This is for small batch, hand or reflow oven soldering. 

All the PCB layout packages I've used have had the ability to specify the mask expansion on a part, or pad by pad basis. The actual mechanism may vary by tool, but even in the worst case I could do a custom pad stack and set the mask opening size exactly.   


UPDATE:
 Sorry, I misread the spec,  JLCPCB is actually .2mm min soldermask sliver.





« Last Edit: June 26, 2021, 01:25:44 pm by Skashkash »
 
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